It is known that one can bundle light passing through an optical material such as a crystal or glass, referred to generically herein as dielectric material. The channel through which the bundled light travels is referred to as an optical waveguide. Optical waveguides are described in the literature and can be formed generally by the diffusion of metal ions into dielectric substrate or by effecting an ion exchange with the dielectric substrate. The channels can be defined by masks applied by lithography in a manner similar to the manner in which conductive paths are formed or microelectronic technology or in which local doping creates electronic components.
Optical waveguides are desirable to provide light paths, generally without loss and without scattering between other components, e.g. between optical fibers or electro-optical components, for influencing the light in its bundled form, generally as to its intensity by modulation or attenuation of the light, etc.
When the light derives from certain atomic or ionic sources, the doping ions can amplify the intensity of the light by induced emission. In that case, the optical component may be a light amplifier. This effect is especially pronounced when the amplification takes place in a resonator bounded by reflectors. Such a device operates in accordance with the principles of a laser. The energy required for amplification is either supplied in an optical form (optical pumping) or can be supplied in the case of semiconductor lasers by electrical means. A process of this type is described in Electronics Letters 25, pages 985-986 (July 1989). In this system, a uniformly doped Nd:YAG crystal is provided with additional waveguides having a laser effect by helium implantation.
A work by Lallier et al, at the Integrated Optics and Optical Communication (IOOC) Conference at Kobe, Japan, July 1989, suggests that a Nd:MgO:LiNbO.sub.3 crystal can be provided with a waveguide with the aid of proton exchange. In this case as well a laser effect is observed. These earlier methods for providing an additional waveguide have been limited to light-doping ions such as those of helium and with protons. With light-emission ions in an optical waveguide, therefore, it is possible to amplify selected intensities or construct a laser in the waveguide.
The use of rare-earth ions (e.g. Nd:YAG) or transition metal ions (for example Ti:Al.sub.2 O.sub.3) as doping ions for the production of solid body lasers is known. However, their use has been limited to systems in which the dielectric crystal or glass is doped in the melt so that the entire crystal or glass body is more or less uniformly doped with the rare earth or transition metal ion.
Such uniformly doped laser crystals cannot, however, be utilized effectively in optical paths coupling further components in accordance with waveguide optical principles, such as modulators, light couplers, path branchers and the like, because in such massive components, the laser ions can give rise to undesirable absorption and scattering phenomenon. Furthermore, differently doped structures creating different optical paths are not possible in these systems.
For a number of reasons, therefore, it is advantageous that not the entire crystal body be formed as the amplifier and laser path but rather to limit the light to an optical waveguide of spatially limited character in the crystal body so that the lateral dimensions of the waveguide are comparable to those of optical fibers or waveguides to which the component is to be coupled so that the light can be received with greater precision from an optical fiber or can be delivered to an optical fiber of limited cross section.
A component having such a spatially limited optical waveguide has the following advantages.
1. Substantial reduction of the optical pumping power required.
2. Greater ability to influence the fields in the cavity for mode locking and cue switching.
3. Utilization of nonlinear characteristics for second harmonic generation, differential frequency formation or frequency summing.
4. Excellent capabilities for coupling of the component to other optical waveguides such as optical fibers.